1. Field of the Invention
The invention relates to the production of integrated circuits. More particularly, the invention relates to the removal of edge beads of spin-on materials from substrates used in the production of integrated circuits.
2. Description of the Related Art
In the production of integrated circuits, several methods have been developed to deposit materials onto a substrate. One common method is spin-coating. Spin coating involves depositing a liquid composition onto a spinning substrate to thereby uniformly coat a surface of the substrate. Spin-coating is widely used in integrated circuit fabrication to deposit thin films of organic and inorganic dielectric materials onto substrates for use, for example, as photoresists, anti-reflection layers, intermetal dielectric layers, sacrificial layers, and passivation layers.
During the spin-coating process, the force exerted on the spinning liquid may cause an amount of the liquid to build up on the edge portion of the substrate forming an edge bead. Portions of the edge bead may detach from the substrate and become a source of particulate contamination during later process steps. Consequently, an area at the edge of the substrate and including the edge bead is typically cleared of coating material in an edge bead removal process during or after the spin-coating process.
In conventional edge bead removal processes, such as disclosed in U.S. Pat. No. 4,732,785, a stream of solvent is directed onto the substrate edge while the substrate is spinning. The solvent stream dissolves and removes a portion of the spin-on film including the edge bead.
Conventional edge bead removal processes suffer from several drawbacks. For example, when the substrate is a semiconductor wafer, conventional edge bead removal processes require a process time of about 5 seconds to about 20 seconds per wafer. A shorter process time would be advantageous. Moreover, the solvents used in conventional edge bead removal processes add to the volume of waste generated in the integrated circuit fabrication process.
In addition, conventional edge bead removal processes can produce unsatisfactory results if the spin-on material contains a solvent with low volatility. Typically, spin-on materials containing low volatility solvents, such as precursor compositions for low dielectric constant nanoporous silica films, are still liquid at the end of the spin-on process. In a conventional edge bead removal process, the solvent used to remove the edge bead is subsequently dried while the substrate is spinning. During the drying period, a spin-on film containing a low volatility solvent can spread back into the region from which the edge bead was removed. Consequently, the region from which spin-on material is removed must be sufficiently wide to compensate for spreading of the spin-on film. This reduces the usable surface area of the substrate.
What is needed is a rapid, environmentally benign edge bead removal process for use with spin-on materials containing low volatility solvents.
Methods are provided for removing edge beads from spin-on films. A spin-on film is removed from a region of a surface of a spin-coated substrate adjacent to an edge of the surface by spinning the spin-coated substrate, expanding a fluid through a nozzle to form a cryogenic aerosol stream, and directing the cryogenic aerosol stream against the spin-on film in the edge region as the substrate spins. The film may include an alkoxysilane and a low volatility solvent.
In another aspect of the invention, a film is formed on a surface of a substrate by dispensing a liquid composition onto the surface, spinning the substrate to distribute the liquid composition to form a substantially uniform film on the surface, expanding a fluid through a nozzle to form a cryogenic aerosol stream, and directing the cryogenic aerosol stream against the film in a region of the surface adjacent to an edge of the surface as the substrate spins. The liquid composition may include at least one alkoxysilane and at least one solvent with a boiling point greater than about 175xc2x0 C.
In one implementation, the fluid consists essentially of liquid carbon dioxide, and the cryogenic aerosol stream includes gaseous carbon dioxide and substantially solid carbon dioxide particles.
Advantageously, no high speed solvent spin-dry step is required during edge bead removal. Consequently, a spin-on film containing low volatility solvents does not grow back into the region from which the film was removed. Also, the edge bead removal process time can be reduced to less than about 10 seconds and a higher throughput can be achieved. Moreover, the volume of waste solvent is reduced and the integrated circuit manufacturing process is thereby made more environmentally friendly.